Digital three-dimensional manufacturing, also known as digital additive manufacturing, is a process of making a three-dimensional solid object of virtually any shape from a digital model. Three-dimensional printing is an additive process in which one or more printheads eject successive layers of material on a substrate in different shapes. Three-dimensional printing is distinguishable from traditional object-forming techniques, which mostly rely on the removal of material from a work piece by a subtractive process, such as cutting or drilling.
Previously known three-dimensional object printers and many two-dimensional printers arrange multiple printheads in a column aligned with a process direction to eject material drops in swaths. These printers typically move the printhead array back and forth over a part or substrate. Small shifts in the cross-process direction are made between passes if multi-pass printing of each swath is necessary and larger shifts are made to print the next swath adjacent to the first swath, if the image or part area is wider than the width of a single swath. The speed or productivity of these devices depends on the width of each swath, which depends on the width of the printheads in the array. An example of a printer that uses swath printing is shown in FIG. 8. In the figure, an array of printheads 104 is arranged in a column aligned with the process direction P and is configured for reciprocating movement in the process direction. The printheads in the array 104 are oriented to eject drops of material onto surface 108, which can be a platen on which a part is produced in a three-dimensional object printer or a media substrate in an inkjet printer. A controller operates an actuator to move the array of printheads from position A to position B while operating the printheads to eject drops of material from the printheads. Small movements of the printheads in the cross-process direction, which is orthogonal to the process direction P, can be used to increase the resolution of the drops in the swath. Once the printing of the swath is complete, the controller operates the actuator to move the array of printheads in the cross-process direction by a distance is approximately equal to a width of the printheads in the array 104. This movement to position C enables the controller to operate the actuator and the printheads to form the second swath adjacent to the first swath.
The productivity of the system shown in FIG. 8 can be increased by increasing the width of the printed swath. Unfortunately, alignment of the ejectors in the rows of the printheads becomes more difficult as the length of the rows increases. The width of the printed swath can be increased without encountering this issue by adding printheads to the array 104. Printheads cannot be butted end-to-end, however, because a printhead housing is wider than the array of ejectors in the printhead so the printheads are typically staggered in the array 104′ as shown in FIG. 9. This structure drastically increases the length of the printhead array in the process direction, which increases the time for each pass between positions A and B in the process direction since longer travel time is required. Therefore, configuring a printhead array to reduce the time required for printing an image or forming a part without increasing the length of the printhead array would be beneficial.